The present invention relates to a gage for thrufeed centerless grinding and in particular to a floating contact gage which measures work pieces exiting the grinder without the necessity of fixturing the work piece during gaging.
Thrufeed centerless grinding is used for high volume precision grinding of outside diameters of everything from continuous stacks of washer-like pads to long thin rods. There are several advantages to this type of grinding. One advantage is the automatic flow of work pieces through the machine, back to back, as if one long work piece was being ground. Another advantage of thrufeed centerless grinding is the ability to improve the roundness of a work piece as it is being ground to finished size.
During grinding, the work piece is supported by a grinding wheel, a regulating wheel and a work rest blade. This would be a desirable place to locate the gage due to the work piece stability provided by the grinding and regulating wheels and the work rest blade. In addition, the gage output can be used to directly control the grinding operation on the gaged work piece. However, due to these machine elements which provide support to the work piece, it is difficult to use an electronic contact gage. There is simply no room to install a gage at a location that will measure the finished part size while it is still between the regulating and grinding wheels. As a result, most centerless grinding gages are "post process" gages. Finished pads are gaged after they have left the grinder. Here, too, there are several difficulties to be overcome. Most post process gages confine the work piece in a fixture during measurement. However, in a thrufeed centerless grinder, work pieces are constantly moving through the gage while being measured. The accuracy of the gaging process can be seriously compromised by the moving work pieces. The moving work pieces must be stabilized relative to the gage in order to obtain accurate gage readings. The gaging of long rods is particularly difficult as the fixture necessary to stabilize the work pieces must grow in proportion to the length of the work pieces.
Accordingly, it is an object of the present invention to overcome the above problems with post process gaging in a thrufeed centerless grinder.
Manufacturers of long centerless ground work pieces usually employ a belt type conveyer to remove the work pieces from the exit of the grinders as they are finished. The present invention provides a gage which is able to contact these work pieces while they are moving along the belt conveyer without requiring any special stabilizing fixture for the work piece. Instead, the gage itself is stabilized by the work piece, enabling the desired gaging accuracy to be achieved. This is accomplished by allowing the gage to float so that it will track the immediate cross-section of the work piece being measured. Non-fixtured moving part gaging has been previously performed in the context of a non-contact gage. These types of gages include laser scanning and air gaging. Both of these gaging methods have their own drawbacks. In post process gaging, following grinding, debris and coolant fluid often remain on the work pieces and adversely affect the gaging accuracy. With non-contact gages, the relative positioning of the work piece and gage is not as critical as with a contact gage.
The gage of the present invention is mounted to a fixture adjacent to the conveyer carrying the work pieces from the grinder. The fixture has a first portion which is stationary and preferably attached to the conveyer structure. A second fixture portion is rotatably attached to the stationary portion and rotates about an axis which is parallel to the path of travel of the work pieces exiting the grinder. A third fixture portion is rotatably mounted to the second portion for rotation about an axis that is normal to the first axis and normal to the path of travel of the work pieces. This second axis, however, is not in the same plane as either the path of travel or the first axis and does not intersect either the path of travel or the first axis. A contact gage is then mounted to the third fixture portion and is thus movable by rotation with two degrees of freedom to track the immediate cross-section of the work piece being measured.
Further objects, features and advantages of the invention will become apparent from a consideration of the following description and the appended claims when taken in connection with the accompanying drawings.